Scuba Diving EquipmentScuba divers today are fortunate to have the latest technology available in scuba diving equipment for breathing underwater. It wasn't always so. A hundred years ago, breathing underwater was accomplished by long tubes, sacks of air carried with a diver and many other ingenious methods. But there were problems associated with those methods that modern demand valve regulators and pressurized scuba diving tanks have solved. As you scuba dive deeper the scuba diving pressure increases about 1 atm (one atmosphere) for every 33 feet (10 m). Since air is easily compressed, your lungs and chest muscles have to exert a force to overcome the scuba diving pressure. But that's more difficult if you're breathing, say, free air delivered from the surface. That air remains at 1 atm. In order to help counteract the increasing pressure, pressurized air is needed. In addition to that, as you scuba dive deeper the gases inside your body get compressed a small amount. Air near sea level is about 78% nitrogen, 21% oxygen with small trace amounts of other gases, mostly argon. But that mixture isn't ideal underwater as the pressure changes. It has to be regulated to deliver the proper concentration of oxygen. Modern scuba diving equipment with air delivery systems compensate for these changing circumstances by providing the right mixture and pressure as divers descend. Since most recreational dives are done with scuba diving masks that encloses the eyes and nose, breathing underwater is done mostly through the mouth. That introduces another problem, since the mouth is wrapped around the scuba diving regulators mouthpiece. As you inhale, you take in air. Your body uses that, then exhales the product, part of which is carbon dioxide. Inhale 21% oxygen, exhale 18% oxygen and about 3% carbon dioxide. Carbon dioxide itself isn't toxic as carbon monoxide is, but breathing too high a concentration decreases the relative amount of oxygen you intake. Ultimately, that would result in oxygen starvation. Oxygen starvation leads to light-headedness, disorientation and ultimately death. The scuba regulator and scuba tank system solves that problem too by the simple process of venting the exhaled gas to the surroundings. Since you don't typically exhale through the nose underwater (that would fog the glass and open the face mask to the water), that solution is more clever than it appears. You are breathing out the same mouthpiece and hose you use to breath in. Venting the carbon dioxide to the water requires some ingenious engineering. Today's scuba diving equipment designs are predominantly open circuit 2-stage scuba diving regulators. The original Aqua-lung design by Jacques Cousteau and Emile Gagnan, developed during WWII was only one stage. In either case, air is delivered at a pressure that matches the surrounding pressure of the diver. Inside the scuba tank, air is pressurized to about 200 atm. In the 2-stage design, the first stage regulator reduces the air pressure to around 10 atm. In the second stage, the demand regulator lowers the pressure again to match that of the surroundings. This delivers air at the best pressure to the diver's lungs, in order to counteract the surrounding pressure. Modern air delivery systems provide safe, healthy air to breath with reliable scuba diving equipment. That's a tribute to the years of dedicated effort and inventiveness of scuba diving gear designers.
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